Shishir Mundra

Last Name

Mundra

First Name

Shishir

ORCID

0000-0001-6559-8814

Organisational unit

09593 - Angst, Ueli / Angst, Ueli

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Publications 1 - 10 of 39

Fundamentally understanding carbonation-induced corrosion of steel in environmentally friendly concretes
Albert, Cristhiana; Mundra, Shishir; Isgor, O. Burkan; et al. (2024)
Revista ALCONPAT
The fundamental understanding of the kinetics of carbonation-induced corrosion, considering the role of the concrete pore solution, pore structure, and moisture content, is discussed in this paper. Open questions and promising approaches to clarify them are also discussed. Based on this knowledge, corrosion propagation can be properly included in the service life design of reinforced concrete structures, reconciling the goals for both sustainable and durable structures. One of the primary solutions is employing environmentally friendly cements with lower clinker content, such as those containing supplementary cementitious materials. However, concretes produced with some of these cements are vulnerable to fast carbonation. While traditional approaches focus on preventing concrete carbonation and corrosion initiation, evidence shows that corrosion rates of steel in carbonated concrete do not necessarily compromise durability.
Transformation of 2-Line Ferrihydrite to Goethite at Alkaline pH
Furcas, Fabio E.; Lothenbach, Barbara; Mundra, Shishir; et al. (2023)
Environmental Science & Technology
The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH ≥ 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis, and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life, t1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 h at pH = 14.0. The calculated-first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log10 k = log10 k0 + a·pH3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow redissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.
The influence of silica on the formation of corrosion products in cementitious systems
Furcas, Fabio Enrico; Mundra, Shishir; Lothenbach, Barbara; et al. (2024)
Chloride binding by layered double hydroxides (LDH/AFm phases) and alkali-activated slag pastes: an experimental study by RILEM TC 283-CAM
Gluth, Gregor J.G.; Mundra, Shishir; Henning, Ricky (2024)
Materials and Structures
Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM ‘Chloride transport in alkali-activated materials’ significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS.
Transformation of 2-line ferrihydrite to goethite at alkaline pH
Furcas, Fabio E.; Lothenbach, Barbara; Mundra, Shishir; et al. (2023)
arXiv
The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH >= 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life,t_1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 hours at pH = 14.0. Calculated first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log_10 k = log_10 k_0 + a*pH^E3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow re-dissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.
X-ray computed tomography to observe the presence of water in macropores of cementitious materials
Rossi, Emanuele; Governo, Susanna; Shakoorioskooie, Mahdieh; et al. (2023)
RILEM Technical Letters
Corrosion of steel reinforcement in concrete is a common degradation mechanism occurring in infrastructures worldwide. Even though extensive research has been conducted over the last decades to accurately predict the influence of steel corrosion on concrete durability, a comprehensive understanding of several micro‐scale processes simultaneously involved in the corrosion mechanism is still lacking. The application of X‐ray Computed Tomography (X‐ray CT) can contribute to elucidate these processes, since this technique allows observing the internal status of specimens non‐destructively, over time, and with a spatial resolution in the range of μm. Nevertheless, the relatively low sensitivity of light elements (e.g., hydrogen and oxygen) to X‐ray CT may hinder the observation of solution within the cementitious matrix. This consideration is discussed in this letter. The results of this study show that the detection of solution in macropores (e.g., air voids) through X‐ray CT is not limited by the relatively low attenuation coefficient of the fluid per se, but more by the spatial resolution at which acquisitions are performed and by the dimensions of the porous volume where solution penetrates. The observations reported in this letter may open several opportunities to further study the influence of the moisture conditions of air voids on several degradation mechanisms of reinforced cementitious materials (e.g., steel corrosion, freeze‐thaw damage), which have been rarely investigated with X‐ray CT according to the literature. The application of these findings could significantly deepen the understanding of several micro‐scale processes that affect the durability of reinforced cementitious materials which still need to be elucidated, as further discussed in the present letter.
Kinetics of iron (hydr)oxide precipitation in cementitious materials
Furcas, Fabio E.; Mundra, Shishir; Lothenbach, Barbara; et al. (2023)
Further Reduction of CO2-Emissions and Circularity in the Cement and Concrete Industry, 16th International Congress on the Chemistry of Cement 2023 - ICCC2023
The accumulation of corrosion products throughout the concrete pore network may lead to the development of internal stresses and spalling of the concrete cover, thus facilitating further structural detonation. To gain a more profound understanding of this self-sustaining sequence of events, both the type of corrosion product(s) as well as their rate of formation within the chemical environment characteristic to cementitious materials must be investigated. By employing a combination of time-resolved TGA, XRD, XAS and ICP studies, we show that the formation of the thermodynamically stable end member goethite (α-FeOOH(s)) is preceded by rapid precipitation of 2-line ferrihydrite (2l-Fe(OH)3(s)) at alkaline pH. Over time, dissolution of the amorphous intermediate prompts re-crystallisation of goethite from solution. Here, precipitation rates scale with the H+ activity. Kinetic rate laws deduced from the progression of aqueously dissolved iron and the amount of solid phase(s) present at any time can lead to better reactive transport models that predict the service life of reinforced concrete structures more accurately.
Application of electrochemical methods for studying steel corrosion in alkali‐activated materials
Mundra, Shishir; Samson, Gabriel; Masi, Giulia; et al. (2023)
Materials and Corrosion
Alkali-activated materials (AAMs) are binders that can complement and partially substitute the current use of conventional cement. However, the present knowledge about how AAMs protect steel reinforcement in concrete elements is incomplete, and uncertainties exist regarding the application of electrochemical methods to investigate this issue. The present review by EFC WP11-Task Force ‘Corrosion of steel in alkali-activated materials’ demonstrates that important differences exist between AAMs and Portland cement, and between different classes of AAMs, which are mainly caused by differing pore solution compositions, and which affect the outcomes of electrochemical measurements. The high sulfide concentrations in blast furnace slag-based AAMs lead to distinct anodic polarisation curves, unusually low open circuit potentials, and low polarisation resistances, which might be incorrectly interpreted as indicating active corrosion of steel reinforcement. No systematic study of the influence of the steel–concrete interface on the susceptibility of steel to corrosion in AAMs is available. Less common electrochemical methods present an opportunity for future progress in the field.
Methods for characterising the steel-concrete interface to enhance understanding of reinforcement corrosion: a critical review by RILEM TC 262-SCI
Wong, Hong S.; Angst, Ueli M.; Geiker, Mette R.; et al. (2022)
Materials and Structures
The steel-concrete interface (SCI) is a complex, multi-phase and multi-scale system. It is widely known to influence the performance and long-term durability of concrete structures. However, a fundamental understanding of its properties and effects on corrosion initiation of embedded reinforcing steel remains elusive. This is attributed to its complicated heterogeneity and time-dependent nature, exacerbated by the lack of suitable techniques for systematic and detailed characterisation. This paper, prepared by members of the RILEM Technical Committee 262-SCI, critically reviews available information regarding current methods (laboratory or field-based) for characterising local properties of the SCI that have been identified as governing factors affecting corrosion initiation. These properties include characteristics of the steel such as mill scale and rust layers, and characteristics of the concrete such as interfacial voids, microstructure and moisture content. We evaluated over twenty methods and summarised their advantages, applications and limitations. The findings show a severe lack of well established, non-destructive techniques that are suitable for direct monitoring of the SCI at a representative scale with sufficiently high resolution (spatial, temporal), particularly for moisture related aspects. Several promising novel techniques with significant potential for further development and application were identified and discussed. Finally, we provide several recommendations for future research needs that are required to advance this critically important topic.
Modelling chloride transport in alkali-activated slags
Mundra, Shishir; Prentice, Dale P.; Bernal, Susan A.; et al. (2020)
Cement and Concrete Research

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